Document EP 2,634,884 discloses such a system including, as primary detection means, current sensors for detecting an output over-current of the converter.
In document EP 2,634,884, the implemented monitoring method provides for monitoring measurements delivered by the current sensors in order to detect the occurrence of a short-circuit-type fault, then, in that case, actuating insulating circuit breakers in order to insulate the converter from the electric machine, which, set in rotation by the wheels of the moving railway vehicle, then operates as a current generator.
The securing method next provides for identifying whether the short-circuit is of the internal or external type with respect to the electric machine. If the short-circuit is internal, the method provides for actuating means for short-circuiting the phases of the electric machine (so-called symmetrization operation), by closing the short-circuiting means.
However, this document of the state of the art does not describe how to detect whether a fault having caused the actuation of the insulating circuit breaker is a fault internal to the electric machine.
If the short-circuit at the origin of the over-currents in the branches of the converter is situated downstream from the insulating circuit breaker, i.e., if it is either a short circuit external to the electric machine, for example between the electric cables connecting each branch of the converter to each phase of the electric machine, or a short-circuit internal to the electric machine, opening the circuit breaker does not suffice to insulate the short-circuit from the power supply source, in the case at hand the traction motor, as long as the latter is rotating.
It should be noted that a downstream short-circuit between a phase of the electric machine and the ground can be insulated by opening the insulating circuit breaker. However, such an electric fault can turn into an inter-phase short-circuit, which cannot be insulated by opening the insulating circuit breaker. Here, such a fault is considered a non-insulatable downstream short-circuit.
A short-circuit can be “dead”, when the two conductors are in direct contact with one another, or “non-dead”, when the two conductors do not touch one another directly, but are connected by means of a medium having a certain impedance. In the latter case, the short-circuit results in the formation of a permanent or intermittent electric arc. This type of fault develops an energy leading to the combustion of the components and surrounding materials of the electric arc: vaporization of the material, modification of the properties of the material, etc.
Note that a dead fault can turn into a non-dead fault by overheating and deterioration of the materials of the conductors initially in contact.
A non-dead short-circuit internal to the electric machine can lead to the destruction of the electric machine with risks of fire (appearance of flames: the electric arc is present until consumption of the phase circle) and/or blockage of the rotor (the material of the phase circle is housed in the air gap, thus damaging the freight and releasing the magnets mounted on the surface).